Can I change the default port numbers when running a Kaspa node?

Yes, Kaspa's default RPC and node-to-node ports can both be changed via command-line flags when you start your node. The RPC port is overridden with --rpclisten localhost:<RPC port number> and the node-to-node protocol port with --listen localhost:<node-to-node protocol port number>. If you do change either port from its default, you must also specify those same non-default ports when configuring your wallet daemon and miner — otherwise those components will keep trying to connect on the old default and fail to reach your node. For a beginner, the takeaway is that ports are like apartment numbers: every piece of software connecting to your node needs to know the right number, so changing one means updating all the others too.